1. Field of the Invention
The present invention relates to an apparatus for measuring the refractive power of an eye to be examined objectively. More particularly, the present invention relates to an eye refractive power measuring apparatus having the ability to discriminate the lens opacity of an eye.
2. Description of Related Art
Conventionally, some eye refractive power measuring devices are known which can measure the refractive power of the spherical surface, cylindrical surface, cylindrical axis, and so on of an eye to be examined objectively. Both hand-operated types and auto-operated types have been available, but the auto-operated type is now broadly used. The auto-operated type was first utilized about twenty years ago, and because of several improvements is now a high-accuracy apparatus.
The eye refractive power measuring devices measure the refractive power by projecting a target onto the fundus of an eye to be examined and receiving a reflection from the fundus by a light receiving device (an image sensor etc.). These devices have only been able to measure the refractive power properties of the eye, and factors such as the lens opacity of the eye which affect the light reflected from the eye fundus have usually been overlooked. However, it is necessary to consider the lens opacity and its influence on eyesight under special sight circumstances.
If the lens opacity of the eye to be examined is so great that the measuring light cannot reach to the fundus, prior devices have not been able to determine whether or not the reason is the lens opacity. Such devices have only indicated that it is impossible to measure the eye refractive power. Moreover, in the case of adjusting the prescription for glasses, although a subjective measurement will be taken by using visual charts and a lens system after completing the objective measurement, if the lens opacity is not clearly indicated, the cause of a difference between the objective measurement value and the subjective measurement value may not be known.